Grinding stone



Nov.v 7, 1939. J. E. HAssLER 2,178,855

GRINDING STONE Filed Feb. 19, 19:58

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Inde/775A- Patented Nov. 7, 1939 was I arrasa n Galan-nwo s'roNn John E.Hassler, Portland, Oreg., assignor to Simcnds Worden White Cio., acorporation of Ohio Application ren-nary i9, 193s, seriali No. 191,431

4 Ciaims.

In the manufacture of mechanical wood pulp, it is necessary to grindblocks of wood by means of large kgrinding stones so as to pull out theshort fibers of the wood. At first, it was coms mon practice to makesuch grinding stones of natural stone, but the inherent defects ofnatural stone made them lacking in uniformity and strength. That is, thestones frequently exhibited fracture lines or other defects which causedsaid stones to burst under high speed rotation. Thus, recent eorts havebeen directed toward producing cast or artificial pulp stones or grinderwheels. It is desirable in wheels thus made that they be reinforced,preferably by circumferential reinforcing rods or bars, so that if thewheel should burst, the central pieces will not iiy out and damage theoperating parts of said pulp grinder or injure workmen employed thereat.

y Bolts of Wood are held against the peripheral grinding surface of apulp wheel under substantial pressure. The friction of the grindingstones upon the wood generates heat within said stone, and it takes asubstantial period of time for said heat to equalize itself throughoutthe entire stone. Thus, the peripheral portions of said stoneV areheated to a greater degree than the central portions thereof, anddifferential expansion due to said unequal temperatures results. Saidstones are integral, and thus the tendency of 3()V the peripheralsurface to elongate relatively to the remainder builds up rupturingstrains in the stone, frequently causing damage.

The object of my invention is to provide a pulp stone or grinder stoneof this character with means permitting the peripheral portions of saidstone to elongate with relation to the central portions thereof withoutsetting up said rupturing strains. My invention has particularapplication to pulp stones or other grinder wheels in which the stone iscast of grit particles embedded in cementitious material and in whichcircumferenential reinforcing elements are located inwardly from theperipheral grinding surface of the stone. Said reinforcing material isspaced inwardly from 45 the peripheral surface of the stone as it isoriginally formed, to a point within the maximum permitted wear of saidstone.

Said object is attained by forming a plurality of uniformly spacedradial slots extending in- 50 wardly of the peripheral grinding surfaceof 4said stone and preferably laterally the full width of the grindingsurface and the full thickness of the grinding portion from saidreinforcing material outwardly so that said grinding portion mightelongate with relation to the central portion without setting uprupturing strains in said stone. Said radial slots preferably are filledwith some resilient composition or material which is preferably plasticso that it Will yield readily under relative elongation, but will flowor move back when the slots are extended *toI their original width. Saidfilling material is desirable so that said slots cannot become lled withforeign inatter and so that the grinding surface of the wheel will besubstantiallycontinuous.

The details of my invention are hereinafter described with reference tothe accompanying drawing, in which: Fig. 1 is an elevation of a pulpstone embodying my invention with a portion thereof shown broken away todisclose the manner in which the radially extending expansion' slots areformed inwardly from the grinding surface of said pulp Wheel Fig. 2 isan elevation of a lpulp wheel embodying my invention with a part shownin section, said figure being taken on the line 2 2 in Fig. l; Fig. 3 isa more or less diagrammatic detail View showing the normal arrangementof one of said slots when the grinding surface is not expanded; and

Fig. 4 is a similar detail view illustrating the vmanner in which thecementitious body of the pulp wheel adjacent said expansion slots ispermitted to expand and to contract the expansion slots and the plasticmaterial with which said slots are filled.

A pulp wheel embodying my invention'comprises a cementitious cast body ain which reinforcing material b is imbedded circumferentially but spacedsubstantially from the grinding sur-` face a of said body. A grinderwheel of this character is adapted to be mounted upon a rotatable shaftc, the body being supported by a central flanged collar d.. to whichcollar the body is secured by threaded bolts or studs e; rI'he sidefaces a2 of said body are engaged by a pair of opposed collars f. Saidcollars preferably are arranged with inwardly extending lateral hub pordtions f extending into the'central bore g of said body. Said collars fengage the side faces of said body and are held tightly there against bythe threading 0f said collars j upon the threaded portion c' of theshaft.

Extending radially inwardly from said grinding surface are a series ofuniformly spaced radial slots h. Said slots extend the f-ull width ofthe pulp stone, as is shown in Fig. 2, and extend substantially the fullthickness of the grinding portion a3 of said stone. The grinding portiona3 55 of said stone is that portion extending outwardly from thereinforcing material b. That is, when said stone is worn down to a pointadjacent the reinforcing material, it is considered to have outlived itsusefulness. The wearing down of the pulp stone correspondinglydiminishes the radius thereof, and when the stone is worn down to suchsmall diameter that the reinforcing material is exposed, it is thrownaway.

Said radial slots are preferably filled with some plastic resilientmaterial such as an asphaltic composition. Said sections i of plasticmaterial prevent foreign -matter from becoming lodged within the radialslots and also bridge over the gap which would be left in the grindingsurface if said sections were not in place. If said slots were notfilled, it would be possible for them to be filled up and the materialto become lodged therein to such a degree that it would prevent thestone from expanding freely and permit said expansion slots fromfunctioning. When said stones are operated, the friction generated byapplying the grinding surface to a block of wood relatively causes thesaid surface to become heated substantially greater than the centralportions thereof. A cast stone of this character is a poor conductor ofheat, and thus relatively severe differential expansion takes place insaid stone.

To limit the absorption of heat in the stone, it is common practice torun water over the face of the stone during the grinding operation. Thewater not only functions to cool the stone but carries away the smallshredded fibers ground off. It is impractical, however, to providesufficient water to keep said stone cool, because this would produce toothin a pulp stock. Of course, after a long operating period, the stonebecomes more or less uniformly heated and the central portions areheated somewhat similarly to the periphery, thedifferential expansionwhich produces rupturing strains is eased, and the expansion slots taketheir original shapes. As is shown diagrammatically in Fig. 4, the slotshave a normal width at. Under induced increase in temperatures,particularly at the grinding surface a', said slots may narrow to awidth y under the stresses imposed by differential expansion. Uniformtemperature throughout the stone, yof course, will cause said slots toapproximate their original Widths.

I claim:

1. A pulp grinding stone comprising an integral cylindrical body havinga peripheral grinding surface, and a plurality of uniformly spacedradial slots extending inwardly from said grinding surface, the totalwidth of said slots being proportioned to accommodate the overallgreater relative circumferential expansion of the grinding surface ofsaid stone than the remainder thereof in the presence of increasedtemperatures set up in said stone by the heat generated in grinding,said slots being lled with a plastic composition adapted to yield undersaid greater relative Vcircumferential expansion.

2. A pulp grinding stone comprising an integral cylindrical body havinga peripheral grinding surface, and a plurality of uniformly spacedradial slots extending inwardly from said grinding surface, the totalwidth of said slots being proportioned to accommodate the overallgreater relative circumferential expansion of the grinding surface ofsaid stone than the remainder thereof in the presence of increasedtemperatures set up in said stone by the heat generated in grinding,said slots being lled with a resilient composition` adapted to yieldunder said greater relative circumferential expansion.

3. A pulp grinding stone comprising an integral cylindrical body havinga peripheral grinding surface, and a plurality of uniformly spacedradial slots extending inwardly from said grinding surface, the totalwidth of said slots being proportioned to accommodate the overallgreater relative circumferential expansion of the grinding surface ofsaid stone than the remainder thereof in the presence of increasedtemperatures set up in said stone by the heat-generated in grinding,said slots being lled with an asphaltic composition adapted to yieldunder said greater relative circumferential expansion.

4. A cast pulp grinding stone comprising an integral cementitiouscylindrical body having a peripheral grinding surface, said stone havingcircumferential reinforcing elements embedded therein lying inwardlyfrom said grinding surface a substantial distance, the portion 0f saidgrinding stone lying between said reinforcing elements and said surfaceconstituting the active grinding portion of said stone, and a pluralityof uniformly spaced radial slots extending inwardly from said grindingsurface, laterally the full width thereof, and the full thickness ofsaid grinding portion, the total width of said slots being proportionedto accommodate the overall greater relative circumferential expansion ofthe grinding surface of said stone than the remainder thereof in thepresence of increased temperatures set up in said stone by the heatgenerated in grinding, said slots being lled with a plastic, resilient,asphaltic composition adapted to yield under said greater relativecircumferential expansion.

JOHN E. HASSLER.

